Photoconductors and method of making the same



United States Patent 3,341,472 PHOTOCONDUCTORS AND METHOD OF MAKING THESAME William A. Hewett, Saratoga, and Alfred H. Sporer, San

Jose, Calif., assignors to International Business Machines Corporation,New York, N.Y., a corporation of New York No Drawing. Filed Aug. 26,1963, Ser. No. 304,687 19 Claims. (Cl. 252-501) The present inventiongenerally relates to photoconductors and more particularly relates tonew organic polymeric photoconductors and method of making the same.

Photoconductors exhibit changes in electrical conductivity upon exposureto radiation of a given wavelength. The usual photoconductors areinorganic semiconductors, However, a few of the newer photoconductorsare organic in nature. Photoconductors have a number of actual andpotential uses, for example as components in various types ofphotoelectric cells and similar instruments, variable resistorcomponents and the like.

Photoconductors have particular application in electrophotographicprocesses, that is, processes where an electrostatic latent image orcharge pattern is formed. Such latent image is then developed to avisible image in a suitable manner, after which the visible image isthen fixed or made permanent.

The electrostatic latent image is usually formed on the surface of aphotoconductive insulating layer which, in turn, may be disposed on asuitable substrate or support. For example, photoconductive material canbe dispersed or dissolved in a suitable medium in admixture with abinding agent. The dispersion or solution can then be coated on asuitable support material and, when dried, the resulting film can beused as the photoconductive insulating layer. The surface of this layercan then be charged in the dark, for example, by means of a coronadischarge. The resulting charge on the surface of the layer issubstantially retained because of the low electrical conductivity of thelayer in the dark. However, upon exposure of the layer to a pattern oflight, for example a lens-projected light image, the photoconductivityof those portions of the layer which are exposed to the light increasesso that the surface charge in those exposed areas leaks away, leavingthe charge only on the unexposed, that is the unilluminated, surfaceareas of the photoconductive layer. This charge pattern constitutes theelectrostatic latent image.

The latent image can be developed by any suitable means, for example bycoating the layer with an electros copic powder which adheres only tothe charged areas of the layer. Such powder may contain, for example, apigment and a heat-softenable resin, so that the image can then be madepermanent merely by heating the powder to above the softening point ofthe resin, causing the resin to permanently adhere to the underlyingmaterial. Such underlying material may be a part of the originalphotoconductive layer or the original support for that layer or a secondsupport to which the powder image is first transferred before heating itup to above the softening point of the resin. Cooling of the powderimage to below the softening point of the resin solidifies the image.

It is of considerable importance in electrophotographic processes tomaximize conditions so as to obtain high quality images. One factorwhich affects the quality of the image is the nature of the bindingmaterial which is usually present with the photoconductive material orphotoconductor in the photoconductive layer. Thus, the binding materialmust be carefully selected so that it does not materially interfere withthe formation, development and fixation of the image. Moreover,ditficulties may 3,341,472 Patented Sept. 12, 1957 arise because of theparticular distribution of particles of the photoconductive materials inthe photoconductive layer and the spatial relationship of suchphotoconductive material to the binding material. The net result is thatin many instances with such systems, it is relatively diflicult toobtain uniformly high quality, sharp, clear developed images.

A few of the newer types of photoconductive materials which are of anorganic nature do not require admixture with binding agents in formingthe photoconductive layer. Instead, certain of these photoconductors canbe formed into films by heating the materials to above the meltingpoints thereof, or by dissolving the same in organic solvents, formingthe film and evaporating the solvents. The resulting films arecontinuous and strongly adhere to substrates. Moreover, in a fewinstances, the photoconductive materials can be effectively used withoutany substrate or support. At least one of these newer photoconductivematerials with the indicated improved characteristics is in the form ofa polymer. However, the polymer is characterized by having a relativelyhigh melting point so that when it is desired to dissolve crystals ofthe polymer in a suitable solvent or to heat the polymer to above thesoftening point thereof in a film-forming operation, con-. siderableheat for a substantial period of time must be employed. Moreover,careful selection must be made with respect to the nature of otheradditives, for example solvents, thinners, etc. so that they canwithstand the high temperatures to which the polymer must be subjectedin order to convert this to a film. Moreover, such polymer is furthercharacterized by having only a limited range of physical characteristicsand being highly selective with respect to the materials with which thiscan be copolymerized. Accordingly, the possible polymeric compoundswhich can be prepared incorporating such polymer and the physical andchemical properties of such compounds are limited, so that suchcompounds are not adaptable to a wide variety of applications asphotoconductive materials. Furthermore, such polymer is relativelydifficult to provide in an ordered or tactic polymeric form which wouldtend to enhance its inherent photoconductivity.

Accordingly, it is a principal object of the present invention toprovide improved crystallizable polymeric photoconductive materials.

It is also an object of the present invention to provide organicpolymeric photoconductors which can be readily prepared in acrystallizable form and as thin films at relatively low temperatures,and method of making the same.

It is a further object of the present invention to provide new organicpolymeric photoconductors which can be readily copolymerized with a widevariety of materials to prepare products having a wide range of physicalcharacteristics.

It is a still further object of the present invention to provide new lowmelting point polymeric photoconductors which have improved film-formingcharacteristics, and method of making the same.

These and other objects are accomplished in accordance with the presentinvention by providing new polymeric photoconductors which includeselected 9-alkenyl substituted carbazole polymers, The polymers havealkenyl substituents with carbon chain length of 4 to 23 carbon atomsand are readily crystallizable. Moreover, the polymers can haverelatively low melting points and can be readily prepared ashomopolymers and as copolymers. The copolymers may be formed bycopolymerizing two or more selected 9-alkenyl substituted carbazoles orby copolymerizing a 9-alkenyl substituted carbazole with a polymerizablematerial of a different type. Such polymerization reactions can becarried out effectively utilizing a wide variety of catalysts, and theextent of polymerization can be readily controlled so that the physicalcharacteristics of the polymers and the photo-conductors preparedtherefrom can be varied within wide limits.

The photoconductors of the invention can be made simply, efficiently andrapidly from such polymers in accordance with the present method. Suchmethod includes sensitizing selected poly-9-alkenyl substitutedcarbazolecontaining material with selected sensitizing agents whichincrease the sensitivity of the product to radiation within the visibleand/or ultraviolet regions of the photospectrum. As an example, an imroved photoconductor was prepared by, sensitizing poly-9-(4-pentenyl)carbazole having the following structural formula:

where m indicated the number average monomeric chain length and Wasabout 500. As a practical matter, the individual polymers in thepolymeric mixture have monomeric chain lengths which can vary from arelatively low monomeric unit multiplication number to a relatively highmonomeric unit multiplication number. The poly-9-(4- pentenyl) carbazolewas sensitized by mixing it with about 3 percent, by weight, of2,5-diphenyl quinone, after dissolving the polymer in a solvent, andthen coating the resulting wet mixture on an aluminum plate and dryingit. The dried and set film was then charged in the dark with 280 voltsfrom a corona unit. The sensitizer conplexed with the aromatic units ofthe polymer so that the product exhibited a charge transfer absorptionband in the visible region of the photospectrum. Accordingly, when thecharged film was exposed to visible light radiation from a high pressuremercury arc lamp, the electrical conductivity of the product rapidly andsubstantially increased, resulting in a dissipation of about one-half ofthe 280 voltage potential (from the surface of the film) in 16.7milliseconds.

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of preferred embodiments of the invention.

It has now been discovered that the photoconductors of this inventioncan be easily prepared from selected crystallizable organic polymers,the physical characteristics of which can be readily controlled. Themechanism of action of the present organic photoconductors is not fullyunderstood. However, it is believed, although the present invention isnot limited to this belief, that in the polymeric photoconductors of thepresent invention, the change in electrical conductivity in response toexposure to radiation of a selected wavelength may be due to thepresence of a specific absorption center in the photoconductivematerial. Thus, an electron donor layer comprising selected donormolecules may be in intimate contact with an electron acceptor layercomprising selected acceptor molecules, and electron transfer may occurfrom the donor molecules to the electron acceptor molecules. Irradiationin a particular absorption band of the photoconductor or in a bandproduced by the addition of sensitizer to the photoconductor results inthe production of charge carriers.

In accordance with the present method, the aromatic units of theselected polymers are complexed with selected photosensitizers. Thephotosensitizer molecules act as acceptor molecules, while the aromaticunits of the polymer molecules act as the donor molecules, thedonoracoeptor interface occurring at the sites where the sensitizermolecules complex with the polymer aromatic units.

The positive charges can be passed between aromatic unit sites withinand between respective polymer molecules, and negative charges can bepassed between sensitizer or other trapping sites within and between therespective polymer molecules.

Although the described manner of operation of the polymericphotoconductors of the invention is considerably simplified andtheoretical, the improved photoconductivity of the present organicphotoconductors is substantial and reproducible.

Now referring more particularly to the present method, polymericmaterials containing new selected 9-alkenyl substituted carbazolepolymers are sensitized with selected sensitizing agents. These polymershave the following general structural formula:

where n: l-20 and m is the number average monomeric unit multiplicationand where R, R, R", R'" and R-"' are substituents selected from thegroup consisting of hydrogen, alkyl, aryl, and substituted alkyl andaryl substituents. Usually, m will vary between about 70 and 1000.However, it is also within the scope of the present invention, andseveral examples are directed thereto, to provide a much lower numberaverage monomeric unit multiplication, for example, as low as 10. Allthat is required is that m be sufficiently high so that it is possibleto form a thin film from the polymer. The minimum m number Willtherefore vary, depending upon the particular polymer employed, itsmolecular weight, etc.

The methods of preparation of this new class of polymers are moreparticularly set forth in copending United States Patent applicationSer. No. 304,697, filed on Aug. 26, 1963, by William A. Hewett andentitled, Polymeric Materials and Methods of Making the Same, the saidapplication having been assigned to the assignee of the presentapplication. As set forth in that application, the polymers may behomopolymers, copolymers, block copolymers and the like, and suchpolymers can be in tactic or .atactic form. A distinct advantage ofthese polymers is that they can be readily prepared in crystallizableform and that they can be easily converted, in accordance with thepresent method, to film form for use in photoconductors inelectrophotographic process. In accordance with the present method, thepolymeric material which is sensitized must contain monomeric unitshaving the following structural formula:

Lli 1 1 lm where n=1-20 and R, R, R", R', and R are substituentsselected from the group consisting of alkyl, aryl, hydrogen andsubstituted alkyl and aryl substituents. Preferably all monomeric unitsof the polymeric material used in the photoconductors fall within thedescribed structural formula. However, selected 9-alkenyl substitutedmonomers can be copolymerized with other polymeric-forming materials,such as propylene, ethylene or the like to provide copolymers havingfilm-forming number average monomeric unit multiplications of, forexample, 70-1000,

as previously indicated, and containing at least some monomeric units ofthe above structural formula.

The polymerization reaction by which the selected 9- alkenyl substitutedpolymers are prepared is carried out in suitable reaction media, such asa solvent for the selected 9-alkenyl substituted carbazole monomer, forexample, hexane, benzene, toluene, tetrahydrofuran or the like, and inthe presence of a suitable polymerization catalyst, for example, of theionic(cationic-anionic) or Friedel-Crafts, Ziegler or other type. Thus,for example, the catalyst may be of the Ziegler (Ziegler-Natta) type,such as a complex or titanium trichloride with another substance such asdiethyl aluminum chloride or the like. Alternatively, a cationiccatalyst such as ethyl aluminum chloride can be used.

The polymerization is usually carried out at relatively low temperature,for example, -70 0, and is terminated either automatically or when thedesired monomeric unit multiplication has been eifected, for example, bythe addition thereto of suitable concentrations of hydrogen. The productis then separated from the reaction medium, unreacted substituents andremaining catalyst to provide the desired polymer useful in thepreparation of the photoconductors of the present invention.

As an example, hexenyl carbazole was reatced at 60 C. in benzene in thepresence of a Ziegler catalyst comprising a complex of diethyl aluminumchloride and titanium trichloride (the diethyl aluminum chloride beingin ,a mole ratio of about 2.5 to the titanium trichloride, i.e. 2.5 EtAlCl/lTiCl with the hexenyl carbazole being in a weight ratio to thecatalyst of about 100:1. The polymerization reaction was instituted bycontacting the hexenyl carbazole in the solvent with the catalyst at thepolymerization temperature and at atmospheric pressure, under anhydrous,non-oxidizing conditions.

Selected 9-alkenyl substituted carbazoles for the manufacture of the9-alkenyl substituted carbazole-containing polymers used in thepreparation of the photoconductors of the present invention, can beprepared in any suitable manner. For example, those 9-alkenylsubstituted carbazoles wherein the alkenyl substituents have carbonchain lentghs of to 23 carbon atoms can be prepared as particularly setforth in copending United States patent application Ser. No. 304,688,filed on Aug. 26, 1963 by William A. Hewett and entitled OrganicCompounds and Method of Making Same, now U.S. Patent 3,252,993, saidpatent having been assigned to the assignee of the present application.As set forth in that patent application, such 9- alkenyl substitutedcarbazoles can be prepared by reaction of a 9-a1kali metal carbazolewith a monohalogenated alkene having a carbon chain length correspondingto that desired for the alkenyl substituent of the carbazole at .anysuitable temperature, for example 50 C.

As a typical example, carbazole in tetrahydrofuran is initially reactedunder anhydrous, non-oxidizing conditions with sodium hydride intetrahydrofuran at room temperature and at atmospheric pressure toprepare 9- sodium carbazole having the following structural formula:

The 9-sodium carbazole in the tetrahydrofuran is then reacted at 50 C.and ,at atmospheric pressure under anhydrous, non-oxidizing conditionswith 5-bromopentene-1 in tetrahydrofuran. The S-bromopentene-l has thefollowing structural formula:

The reaction is completed in 1 hour and the desired product,9-(4-pentenyl) carbazole, is obtained in a yield of about 607 9 alkenylsubstituted carbazoles having alkenyl substit-uents with a carbon chainlength of four carbon atoms cannot be prepared by the indicatedcondensation procedure. Instead, those carbazoles must be prepared by adifferent route, such as that set forth in copending United Statespatent application Ser. No. 304,696, filed on Aug. 26, 1963, by JorgeHeller and entitled Organic Compounds and Method of Making Same, now U.S. Patent No. 3,268,550, said patent having been assigned to theassignee of the present application. As: more particularly set forth inthat application, in order to prevent the formation of butadiene typeproducts, it is necessary to prepare 9 (3 butenyl) carbazoles by firstcondensing under anhydrous, non-oxidizing conditions 9-a1kali metalsubstituted carbazole (sodium, potassium or lithium carbazole) with 1,4dihalogenated butane, wherein the halogen atoms are selected from thegroup consisting of chlorine, bromine and iodine atoms. Such reactionmay be carried out in the presence of a suitable catalyst, and theproduct is a 9 (4 monohalogenated butyl) carbazole. This product is thendehydrohalogenated under anhydrous, non-oxidizing conditions in thepresence of a suitable catalyst, such as potassium tertiary butoxide,that is, potassium in tertiary butyl alcohol, at about refluxingtemperature, that is, under rather severe dehydrohalogenatingconditions, to produce 9 (3 butenyl) carbazole.

As an example, sodium carbazole has been reacted with 1,4 dichlorobutaneunder anhydrous, non-oxidizing conditions to produce 9 (4 chlorobutyl)carbazole, the reaction taking place in the presence of sodium iodideand while the constituents were disposed in anhydrous tetrahydrofuran.The resulting 9 (4 chlorobutyl) carbazole has been dehydrohalogenatedunder anhydrous, non-oxidizing conditions at refluxing temperature to 9-(3 butenyl) carbazole while in teriary butyl alcohol along withpotassium. It has been found that similar carbazoles which, however,carry substituents (alkyl, aryl and/or alkylaryl) on the 3-butenylsubstituent can be prepared by the same method. The 9 (3 butenyl) typecarbazoles can also be made by other procedures.

The selected sensitizer utilized in the method of the present inventionfor the preparation of the new photoconductors, is any sensitizer whichis capable of complexing with the aromatic units of the above-describedpolymer so that the product exhibits increased photosemiconductivecapacity in the near ultra-violet and/or visible light portions of thephotospectrum. The sensitizer renders the polymer photosensitive in thenear ultraviolet and/or visible light portions of the photospectrum sothat it becomes a suitable photoconductor for a variety of purposes.Also as previously described, the sensitizer acts to provide electronacceptors and cooperates with the polymer to provide donor-acceptorinterfaces in the form of a charge-separating complex. Many types ofcommercially available sensitizers can be used in the present method.They include, but are not limited to, quinones, such as 2,5-diphenylbenzoquinone, benzoquinone, di-ter-tiary butylbenzoquinone,anthroquinone, duroquinone, and phenyl benzoquinone. They also includeother materials such as unsaturated acid anhydrides, for example,pyromellitic dianhydride.

In addition, various types of polynitro compounds can be used. Forexample, polynitroethylene, polynitrobenzene, polynitrotoluene andpolynitroxylene. Moreover, various polycyano compounds can be used, forexample, tetracyanoethylene, polycyanobenzene, polycyanotoluene andpolycyanoxylene. In addition, other photosensitizers such as iodine,O-chloranil, boron trifluoride, ferric chloride and diethyl aluminumchloride can be used.

In accordance with the present method, the sensitizer is complexed withthe polymer. Any suitable amount of sensitizer can be used depending onthe particular polymer and sensitizer.

In order to facilitate complexing of the sensitizer with the polymer,the sensitizer is intimately and uniformly dispersed throughout thepolymeric material. The dispersal can be effected by any suitableprocedure, for

example, ball milling the polymer and sensitizer in a suitable solventfor the polymer and the sensitizer until the sensitizer is dissolved.Such solvent may be, for example, toluene, benzene, xylene, methylpyrrolidone, methyl ethyl ketone, methylene chloride or the like. Theball milling is carried out at solvent temperatures ranging up to theboiling point of the solvent. It will be noted that relatively lowboiling point solvents can be used without difiiculty, particularly withthose polymers which have low monomeric unit multiplications. This is incontrast to prior higher melting point, more difficultly solublephotoconductive polymers. Alternatively, the polymers can be heated to arelatively low temperature, in contrast to prior photoconductivepolymers, to render them viscous, whereupon the dispersal is effected bystirring the sensitizers into the viscous polymers. For example, apowdered mixture of a selected polymer and sensitizer can be melted at,for example, about 190 C.

The resulting improved photoconductor can, if desired, then be directlyapplied as a thin film on a suitable support or substrate, such as analuminum plate, and can then be allowed' to dry or solidify. Thus, forexample, poly 9 (4 pentenyl) carbazole can be sensitized with 2,5diphenyl benzoquinone (4% concentration, by weight), the mixture alsocontaining methylene chloride, whereupon the mixture can be coated on analuminum or other electrically conductive base plate. The desired filmthickness will vary, depending on the particular photoconductivematerial, but usually is relatively thin, for example, from about 0.1mil to about 5 mils in the dried state. The dried coating or film canthen be charged in the dark with a corona unit to provide a suitablevoltage potential, which upon subsequent exposure to suitable lightradiation will decay or bleed off rapidly to a given value in arelatively few milliseconds.

Certain features of the present invention are illustrated in thefollowing examples:

EXAMPLE I A novel photoconductor comprising poly 9 (4 pentenyl)carbazole complexed with 2,5 diphenyl benzoquinone is prepared accordingto the following procedure:

Approximately 8.5 gm. of sodium carbazole in 120 ml. of anhydroustetrahydrofuran, previously prepared by reacting under anhydrousconditions and under a nitrogen blanket about 8.4 gm. of carbazole inthe same solvent with about 1.3 gm. of sodium hydride at 35 C. for 1.5hours, is reacted at refluxing temperature under anhydrous conditionsand under a nitrogen blanket with 9 gm. of 5-bromo-pentene-1 in 20 ml.of anhydrous tetrahydrofuran for 20 hours under agitation to provide 6gm. of 9- (4-pentenyl) carbazole. The 9-(4-pentenyl) carbazole in about5 gm. amount is then disposed in 50 ml. of benzene which contains 1%benzoyl peroxide. The temperature of the reactants is then raised to andmaintained at 70 C. for 24 hours under anhydrous conditions until themonomeric unit multiplication is approximately 10. A yield of about 3.5gm. of the polymer is obtained. The polymer is separated from thecatalyst and reaction medium by repeatedly washing it with large volumesof ethyl alcohol. This polymer has an intrinsic viscosity of about 0.03.

The polymer is an intrinsic photoconductor in the ultraviolet region butis further sensitized to the near ultraviolet and visible regions of thephotospectrum by complexing the aromatic units thereof with, aspreviously indicated, 2,S-diphenyl-p-benzoquinone, the latter in aconcentration of 4% by weight. Such sensitization is effected by firstdissolving the poly-pentenyl carbazole in methylene chloride and thenadding the indicated concen- 8 tration of the2,S-diphenyl-p-benzoquinone. The resulting product has a charge transferabsorption band in the blue region of the photospectrum with a darkconductivity of about 0.8% that of its light conductivity, i.e.,conductivity when exposed to light from a high pressure mercury arclamp.

The resulting photoconductor is disposed in the dark while dissolved inthe methylene chloride as a thin film approximately 0.5 mils thick (whendried) on an aluminum plate. It is then dried and is then subjected inthe dark to a voltage of about 300 volts positive. When the charged filmis subsequently exposed to a high pressure mercury arc lamp radiation,the voltage decreases in approximately 6 milliseconds to about volts,indicating a large increase in the electrical conductivity thereof.Accordingly, the novel photoconductor is suitable for use inelectrophotographic processes requiring a photoconductive material uponwhich can be disposed an electrostatic latent image which can bedeveloped to a visible image and fixed.

EXAMPLE II A novel photoconductor comprising poly 9-(4-pentenyl)carbazole having a number average monomeric unit multiplication of about200 is prepared in the following manner:

The 9-(4-pentenyl) carbazole monomer is prepared in accordance with themethod set forth in Example I. The polymer is prepared therefrom byreacting about 4.7 gm. of the monomer while disposed in 40 ml. ofbenzene with a Ziegler catalyst comprising 2 millimoles of titaniumtrichloride and 5 millimoles of diethyl aluminum chloride. The reactiontemperature is maintained at 50 C. for 72 hours under non-oxidizinganhydrous conditions until the desired monomeric unit multiplication ofabout 200 is obtained. Approximately 2.5 gm. of the polymer is obtainedby this method. The so-produced polymer is separated from the catalystand reaction medium by adding the product to a mixture of 20 ml. ofhydrochloric acid in methanol (10% by volume of the product) andstirring the mixture for 15 minutes, after which the product is pouredinto a large volume of methanol and filtered. Such purified product upondrying is found to be in tactic form and have an intrinsic viscosity ofabout 0.40. It is a white powder with a softening point of about C.

In preparing the photoconductor from the poly 9-(4- pentenyl) carbazolehaving a monomeric unit multiplication number of 200, the polymer inpowderform is melted at C. and to it is added about 4% by weight ofphenanthrenequinone. The phenanthrenequinone is uniformly distributedthroughout the melted powder. Upon testing, the resulting photoconductoris found to have a charge transfer absorption band in the blue region ofthe photospectrum. This product in melted form is disposed as a thinfilm approximately 1 mil thick (when dried) on an aluminum plate andwhen the film is solidified, it is subjected in the dark to a voltage ofabout 650 volts positive from a corona unit. The charged film is thenexposed to the radiation from a high pressure mercury arc lamp and it isfound that the voltage decreases in about 29 milliseconds toapproximately 325 volts, indicating an increase in the electricalconductivity of the film of about 8,000 times. Accordingly, the novelphotoconductor is suitable for use in electrophotographic processeswhich require a photoconductive material capable of carrying anelectrostatic latent image and having the image developed in a suitablemanner and fixed.

EXAMPLE III A novel photoconductor comprising poly 9-(4-pentenyl)carbazole having a number average monomeric unit multiplication of about10 and complexed with orthochloranil is prepared in the followingmanner:

The monomer and the polymer are prepared according to the method setforth in Example I. The polymer is then dissolved in methylene chloridein a concentration of about gm. of polymer per 100 ml. of the chloride,after which about 20 mg. of the sensitizer is added thereto. Theresulting photoconductor while still dissolved in the methylene chlorideis coated on an aluminum plate to a coating thickness (dry state) ofabout 0.5 mil. After the coating is dried, it is subjected in the darkto a charge of about 240 volts positive. When the charged film is thenexposed to the radiation from a high pressure mercury arc lamp, thevoltage decreases in about 2.5 milliseconds to about 120 volts,indicating an increase in the electrical conductivity of the fihn ofabout 7,200 times. Accordingly, the novel photoconductor is suitable foruse in electrophotographic processes and the like.

EXAMPLE IV A novel photoconductor comprising poly 9-(4-pentenyl)carbazole complexed with pyromellitic dianhydride sensitizer is preparedin the following manner:

The monomer and polymer are prepared in accordance with the method setforth in Example II, the polymer having a number average monomeric unitmultiplication of about 200. The polymer is converted into an improvedphotoconductor by melting the polymer at 190 C. and adding thereto about4% by weight of pyromellitic dianhydride sensitizer. The resultingmolten photoconductor is then disposed on an aluminum plate to a filmthickness of about 1 mil (when solidified) and is cooled to below thesolidification point thereof. When the solidified film is subjected to acharge of about 630 volts positive in the dark from a corona unit, andthen subsequently exposed to radiation from a high pressure mercury arclamp, it is found that the voltage decreases in about 70 milliseconds toabout 315 volts, indicating an increase in the electrical conductivityof about 1,300 times. Accordingly, the novel photoconductor is suitablefor use in electrophotographic processes and the like which re quire aphotoconductive material which is capable of readily forming into a filmat relatively 'low temperature and which is also capable of retaining anelectrostatic latent image, which image can be developed and fixed.

EXAMPLE V A novel photoconductor comprising poly 9-(5-hexenyl)carbazole, sensitized with phenyl p-benzoquinone sensitizer, is preparedin accordance with the following procedure:

9-(5-hexenyl) carbazole is prepared by reacting 55 gm. of 9-sodiumcarbazole in 800 ml. of anhydrous tetrahydrofuran at about 70 C. underanhydrous conditions and under a nitrogen blanket with 65 gm. of6-bromo-1- hexene disposed in 100 ml. of anhydrous tetrahydrofuran for20 hours under agitation. The product comprises 36 gm. of the9-(5-hexeny-l) carbazole. The 9-sodium carbazole was previously preparedby reacting about 55 gm. of anhydrous carbazole in anhydroustetrahydrofuran with about 9 gm. of anhydrous sodium hydride at 25 C.for 3 hours and under anhydrous conditions under a nitrogen blanket.

About 5 gm. of the 9-(5-hexenyl) carbazole is dispersed in 40 ml. ofbenzene containing 2 millimoles of titanium trichloride, 5 millimoles ofdiethyl aluminum chloride. The reactants are maintained at 70 C. for 2hours under non-oxidizing anhydrous conditions until a polymer is formedwhich has the number average monomeric unit multiplication of about 200.Approximately 26 gm. of the polymer are obtained. On purification thepolymer has a viscosity of about 0.46 and is in the form of a whitepowder with a softening point of about 180 C.

The polymer is converted into improved photoconductor by the followingprocedure:

The improved photoconductor is disposed as a thin film of about 1.5 ml.thickness on an aluminum plate by the following procedure:

The mixture of polymer and 4% by weight phenyl pbenzoquinone wascompression molded into a thin film (approximately 1 mil) on an aluminumsubstrate at 170 C. and 20,000 psi. pressure.

The dry film is charged to a positive voltage of about 860 volts in thedark and upon subsequent exposure of the film to radiation from a highpressure mercury arc lamp, the voltage decreases in about 18milliseconds to about 430 volts, indicating an increase of electricalconductivity of the film of about 1,800 times. Accordingly, the novelphotoconductor is suitable for use in a wide variety of applicationsincluding use as a photoconductive layer in an electrophotographicprocess.

EXAMPLE VI A novel photoconductor is prepared, which photoconductorcomprises poly-9-(22-tricosenyl) carbazole complexed with anitrophenylquinone sensitizer. The method of preparation of the improvedphotoconductor is as follows:

About 8.5 gm. of 9-sodium carbazole in 120 ml. of anhydroustetrahydrofuran, previously prepared by reacting under anhydrousnon-oxidizing conditions about 8.4 gm. of carbazole in the same solventwith about 1.3 gm. of sodium hydride at 23 C. for 1.5 hours, is reactedunder, anhydrous non-oxidizing conditions at about 70C. with 24 gm. of23-bromo-l-tricosene disposed in 40 ml. of anhydrous tetrahydrofuran for20 hours under agitation to provide 10 gm. of 9-(22-tricosenyl)carbazole. This product in 10 gm. amount is disposed in ml. of benzenewhich also contains 2 millimoles of titanium trichloride and 5millimoles of diethyl aluminum chloride. The temperature of the reactantis maintained at 70 C. for 72 hours under anhydrous nonoxidizingconditions until a polymer is produced which has a number averagemonomeric unit multiplication of about 100. This polymer is produced inabout 6 gm. amount. Upon purification, the product is identifiable aspoly-9-(22-tricosenyl) carbazole and is converted to an improvedphotoconductor by the following procedure:

This product is mixed with 4% by weight of 4-nitrophenyl-quinone andthen melted at 130 C. and in the molten condition is coated on analuminum plate and then cooled to below the solidification point thereofto provide a 1 mil thick film in the solid state on the aluminum plate.This film is then subjected to a voltage of about 1,000 volts positivein the dark and when subsequently exposed to radiation from a highpressure mercury arc lamp, this voltage decreases to about 500 volts inabout milliseconds, indicating an increase in the electricalconductivity of the film of about 300 times.

Accordingly, the novel photoconductor has improved properties and issuitable for use in electrophotographic processes and the like. In thisconnection, the novel photoconductor can be disposed as a film, aspreviously indicated, on a suitable substrate and then can be charged inthe dark to a suitable voltage and then exposed to image-wise radiationto which it is sensitive, for example in the ultra-violet region or thevisible light region of the photospectrum. The electrostatic latentimage pattern remaining on the photoconductor film after the imagewiseradiation can be developed by various techniques, such as a conventionaltoning technique and the like. Moreover, the latent image can bedeveloped and rendered visible by a heating technique, such as is usedin thermoplastic recording of electronic beam images. Thus, upon rapidheating of the photoconductor containing the electrostatic latent imagepattern to the melting point of the photoconductor, the electrostaticlatent image remaining on the surface of the photoconductor film causesdeformation of the polymer of the film in the charged areas, resultingin a deformation image which can be detected by a suitable technique.

Accordingly, with this and others of the improved photoconductors of thepresent invention, there is no necessity to employ conventionaltime-consuming toning techniques in order to develop and fix images.Instead, the electrostatic latent image can be used directly to modifythe physical condition of the polymer in the area immediately associatedtherewith so that the desired developing and fixing of the latent imageoccurs in a simple improved manner. Accordingly, the improvedphotoconductors of the present invention have improved versatility inapplications to electrophotographic processes and other systemsrequiring sensitized photoconductive materials.

EXAMPLE VII An improved photoconductor comprising poly-9(10-phenyl-lO-undecenyl) carbazole complexed and sensitized withp-chlorophenylquinone sensitizer, is prepared in the following manner:

The 9-(10-phenyl-10-undecenyl) carbazole is prepared by reacting about8.5 gm. of 9-sodium carbazole in 120 ml. of anhydrous tetrahydrofuran,previously prepared by reacting under anhydrous non-oxidizing conditionsabout 8.4 gm. of carbazole in the same solvent with about 1.3 gm. ofsodium hydride at 23 C. for 1.5 hours, with 18.5 gm. of2-phenyl-1l-bromo-undecene-l in 60 ml. of tetrahydrofuran at about 70 C.under anhydrous non-oxidizing conditions for 20 hours under agitation.About 12 gm. of 9-(10-phenyl-10-undecenyl) carbazole is provided. About5 gm. of this product is then disposed in 60 ml. of methylene chloridecontaining about 0.2 gm. of boron trifluoride etherate catalyst. Thereactants are maintained at 78 C. for 6 hours under anhydrousnon-oxidizing conditions until a polymer is produced which has a numberaverage monomeric unit multiplication of about 12. Thereupon, thepolymerization is discontinued by the addition to the reaction medium ofammonium hydroxide. The produced polymer is then separated from thecatalyst, monomer and reaction medium by repeatedly washing it withmethanol until it is neutral in pH. The polymer is then filtered anddried and is converted into the improved photoconductor by melting it at190 C. and adding thereto about 4% by weight of p-chlorophenylquinonesensitizer and distributing the sensitizer throughout the meltedpolymer.

The resulting improved photoconductor has an absorption band in theultra-violet region of the photospectrum and a dark conductivity ofabout 5% that of its light conductivity when exposed to a high pressuremercury arc lamp light. Such product in the molten state is then coatedas a thin film on an aluminum plate (to a film thickness, when dry, ofabout 1 mil), solidified, and then charged in the dark to a voltage ofabout 900 volts positive. When the charged film is then exposed to ahigh pressure are lamp radiation, the voltage decreases in about 30milliseconds to about 450 volts, indicating a substantial increase inthe electrical conductivity of the film. Accordingly, the improvedphotoconductor is suitable for use for a wide variety of applicationsincluding electrophotographic processes.

EXAMPLE VIII An improved photoconductor comprising poly-9-(4-methyl-4-pentenyl) carbazole sensitized with 2,4,6 trinitrobenzoic acidis prepared in the following manner: Approximately 8.5 gm. of 9-sodiumcarbazole, in 120 ml. of anhydrous tetrahydrofuran solvent, previouslyprepared by reacting under a nitrogen blanket 8.4 gm. of anhydrouscarbazole in the same solvent with about 1.3 gm. of anhydrous sodiumhydride at 23 C. for 1.5 hours, is reacted under anhydrous non-oxidizingconditions at about 70 C. with 10 gm. of 2-methyl-5-bromopentene- 1disposed in 60 ml. of tetrahydrofuran for 20 hours under agitation toprovide 5 gm. of 9-(4-methyl-4-pentenyl) carbazole.

This product, upon separation from the catalyst, reaction medium andunreacted constituents, is disposed in 60 ml. of methylene chloridesolvent which also contains 0.2 gm. of boron trifluoride etheratepolymerization catalyst. The temperature of the reactants is maintainedat 78 C. for 6 hours under anhydrous non-oxidizing conditions, until thenumber average monomeric unit multiplication is approximately 12. Ayield of about 3.5 gm. of poly-9-(4-methyl-4-pentenyl) carbazole isobtained. Thereupon the so-produced polymer is separated from thecatalyst and reaction medium by the following procedure: Repeatedlyworking it with large volumes of methyl alcohol. The purified polymerhas an intrinsic viscosity of about 0.03, and is a white powder.

The poly-9-(4-methyl-4-pentenyl) carbazole is converted to an improvedphotoconductor by complexing the aromatic units of the polymer with, aspreviously indicated, 2,4,6 trinitrobenzoic acid sensitizer, the latterbeing in a 4% by weight concentration, with respect to the product. Thesensitization reaction is effected by the following procedure: Thepolymer is compression molded at C. and 20,000 psi. on an aluminumsubstrate. The polymer is then swelled with a 4% solution of 2,4,6trinitrobenzoic acid in benzene. The resulting improved photoconductionproduct has a charge-transfer absorption band in the ultra-violet regionof the photospectrum, with a dark conductivity approximately 4% that ofits light conductivity, e.g. conductivity when exposed to mercury arelight. Such product is disposed in a thin film approximately 1.5 milsthick on an aluminum plate. The'film is then charged to a voltage ofapproximately 850 volts positive in the dark. When the charged film issubsequently exposed to radiation from a high pressure mercury arc lamp,the voltage decreases in approximately 20 milliseconds to approximately425 volts, indicating an increase in the electrical conductivity of theexposed film of approximately 1,700 times. Accordingly, the improvedphotoconductor is suitable for use in electrophotographic processes andthe like.

The preceding examples clearly illustrate that novel organic polymericphotoconductors which are readily crystallizable and which can bereadily converted into films at relatively low temperatures can beprepared easily, efiiciently and inexpensively in a wide variety offorms and with a wide variety of physical characteristics in accordancewith the present method. The Examples also indicate that variousreaction conditions and techniques can be employed in carrying out thepresent method. The polymers forming a part of the photoconductors canbe homopolymers, copolymers, block copolymers and the like, in tactic oratactic form and having a wide range of monomeric unit multiplication.The sensitizers are those substances which increase the sensitivity orresponse of the photoconductive materials over that of the untreatedphotoconductive materials to radiation in the ultra-violet and/orvisible portions of the photospectrurn. The sensitizers complex with thearomatic units of the carbazolecontaining portions of the polymers sothat the net result is a product which exhibits increasedphoto-semiconductor capacity or sensitivity over that of the untreatedpolymers with respect to near ultra-violet and/ or visible light.

The new and improved photoconductors have particular utility inelectrophotographic processes. However, due to the wide variety ofphysical characteristics which they exhibit, the photoconductors aresuitable for use in other processes and as components of various typesof mechanical and electronic equipment. Various other advantages of thepresent invention are as set forth in the foregoing.

While the invention has been particularly shown and described withreference to preferred embodiments there of, it will be understood bythose skilled in the art that variations in form may be made thereinwithout departing from the spirit and scope of the invention.

What is claimed is:

1. An organic polymeric photoconductor which consists essentially of:

' a'polymer which has the structural formula:

stituents, and

an electron acceptor complexed with aromatic units of said polymer, in aconcentration which effectively increases the photo-semiconductivesensitivity of said polymer to radiation.

2. The photoconductor of claim 1 wherein the polymer is in tactic form.

3. The photoconductor of claim 1 wherein the polymer is in atactic form.

carbazole.

where n=l19, m=l-lO00, and R, R, R", R'" and R"" are substituentsselected from the group consisting of hydrogen, alkyl, aryl andalkylaryl suba 9-(4-pentenyl) carbazole polymer having the structuralformula:

6. An organic polymer photoconductor which consists essentially of:

a copolymer, a major amount of the monomeric units of which has thestructural formula:

H I H H-C--H 10 H( 1N l 1n L H H J wherein m=1000, and an electronacceptor complexed therewith in a concentration sufficient tosubstantially increase the photo semiconductive sensitivity of thepolymer to radiation.

11. A polymeric photoconductor consisting essentially of:

a 9-(5-hexenyl) carbazole polymer having the structural formula:

H|-H H-C-H H- -11 /H I L H H 1 wherein m=701000, and an electronaccept-or compleXed therewith in a concentration suflicient tosubstantially increase the photosemiconductive sensitivity of thepolymer to radiation. 12. The method of making an organicphotoconductor, which method comprises:

complexing aromatic units of polymeric material containing monomericunits having the structural forwherein n=1-19, wherein m=l0l000, andwherein R, R, R, R" and R"" are substituents selected from the groupconsisting of hydrogen, alkyl, aryl and substituted alkyl and arylgroups, said copolymer being crystallizable and,

meric units to radiation.

7. The photoconductor of claim 6 wherein each of the monomeric units ofsaid :copolymer have said structural formula 8. The photoconductor ofclaim 7 wherein said c0- polymer is in tactic form.

9. The photoconductor of claim 7 wherein said copolymer is in atacticform.

10. A polymeric photoconductor consisting essentially mula:

wherein n: l-19, m1=-101000, and wherein R, R, R", R and R"" aresubstituents selected from the group consisting of hydrogen, alkyl, aryland alkylaryl substituents, with an electron acceptor in a concentrationwhich effectively increases the photo-semiconductive sensitivity of themonomeric units to radiation.

13. The method of claim 12 wherein said polymeric material is ahomopolymer containing said monomeric units.

14. The method of claim 12 wherein said homopolymer ispoly-9-(5-hexenyl) carbazole in tactic form.

15. The method of claim 12 wherein said homopolymer ispoly-9-(10-phenyl-10-undecenyl) carbazole in tactic form.

16. The method of claim 12 wherein said homopolymer ispoly-9-(22-tricosenyl) carhazole in tactic form.

15 17. The method of making an organic photoconductor, which methodcomprises:

complexing polymeric aromatic units having the structural formula:

16 photo-semiconductive sensitivity of the polymer to radiation.

18. The method of claim 17 wherein each of the monomeric units of saidcopolymer has said structural formula.

19. The method of making an organic photoconductor comprising complexingaromatic units of a homopolymer of poly-9-(4-pentenyl) carbazole intactic form and having 10-1000 monomeric units, by dissolving saidpolymer in methylene chloride and dispersing about 4%, 'by weight, of2,S-diphenyl-p benzoquinone therethrough.

References Cited UNITED STATES PATENTS 3,037,861 6/1962 Hoegl et al 96-13,155,503 11/1964 Cassiers et al 961 3,232,755 2/1966 Hoegl et a1 961LEON D. ROSDOL, Primary Examiner.

R. D. LOVERING, Examiner.

1. AN ORGANIC POLYMERIC PHOTOCONDUCTOR WHICH CONSISTS ESSENTIALLY OF: APOLYMER WHICH HAS THE STRUCTURAL FORMULA:
 12. THE METHOD OF MAKING ANORGANIC PHOTOCONDUCTOR, WHICH METHOD COMPRISES: COMPLEXING AROMATICUNITS OF POLYMERIC MATERIAL CONTAINING MONOMERIC UNITS HAVING THESTRUCTURAL FORMULA: